even though enanthate ester, and all long esters, have half lifes ranging in the 3-6 week range (some less, some more).. that doesnt mean you will have to wait weeks for effects. the fday you inject 250mgs of test enanthate you will immidietly have over 3 times the normal amount of testosterone in your body, assuming average test levels to begin with.
enanthate releases approx 30mg's on day one, 27mgs on day 2, 25mgs on day 3.. and so on... all the way untill days 10-15, at which point the amounf released drops below 10mgs, and is no longer supraphysiological.
long story short, with real roids, you dont have to wait weeks, but days. in fact you can feel it day two.